The present invention relates generally to a new and improved pipe fitting and method for making same, and more particularly, to a prefabricated, butt-welded double containment pipe fitting.
There is an ever increasing concern today over the environment and particularly to chemical spills and leaks where chemicals are absorbed by the ground and migrate to groundwater. The cleanup of such chemical spills is both costly and tedious. In order to provide some measure of assurance against chemical contamination, the chemical industry, especially the chemical waste processing industry, has adopted the use of double containment pipe and underground storage tanks to convey and store fluid chemicals.
Double containment piping consists of two pipes. Both pipes are typically made of a thermoplastic material because of the high corrosion resistance, low weight and low cost of plastics in general. One pipe of the two pipes is known as the primary pipe and is intended to convey chemical fluids or effluents. The other pipe is known as a secondary pipe and it extends around the primary pipe in a spaced-apart relationship to define an annular space between the primary and secondary pipes.
The secondary pipe provides a protective casing or containment which will contain chemicals escaping from the primary pipe due to leakage and prevent the chemicals from escaping into the environment. Leak detection or monitoring systems may be disposed within the annular space for identifying leaks to the system processing operator.
Prior double containment piping systems were costly and labor-intensive. Double containment piping systems typically required the installation contractor to fabricate much of the system during its installation. This fabrication typically included the fabrication of various fittings such as wye, lateral, tee and reducing fittings. Certain other fittings also were field-fabricated such as elbows and cross fittings. This field fabrication was a costly aspect to any double containment piping system installation. The field fabrication of such fittings was expensive because it required cutting pipe lengths, or spools to obtain various size pipe portions which were then fillet welded together using a thermoplastic welding rod. This process is both time consuming to the contractor and the owner and the quality effected in the field may not be up to the standards of quality that can be readily replicated in a factory situation.
Although some past methods have been known for joining together thermoplastic pipe sections, each method has certain disadvantages. For example, U.S. Pat. No. 3,013,925 issued Apr. 3, 1959 describes a method in which two pipe spools are held together in a vise and their opposing ends are brought into contact with a planar heating element to melt the endwalls of the pipe sections. After heating, the pipe endwalls were brought together and held in place until the plastic cools. This method is only effective for joining straight pipe lengths.
U.S. Pat. No. 4,779,652, issued Oct. 25, 1988, describes a integrally molded pipe fitting which primary and secondary pipes are molded together as one piece and are separate by integral pipe supports molded integrally therewith. Molding the primary and secondary pipe together as a single unit requires a costly investment in molds and this investment may limit the ability of the pipe supplier to supply prefabricated custom fittings in accordance with a contractor""s installation drawings. A mold must be made for each particular style fitting and thereby reduces the likelihood of a cost effective custom fitting being made quickly.
U.S. Pat. No. 5,185,049 which issued Feb. 9, 1993, describes an apparatus for butt-welding double containment pipe sections together by bringing opposing endwalls of the pipes in contact with a hinged planar heating element until the plastic softens, at which time the ends are joined together to form a solid butt-joint. The planar nature of this heating element precludes its use for assembly of complex fittings such as tee, wye, cross or reducing fittings which require detailed calculation of angled mating surfaces.
In order to reduce the amount of labor expended in construction of double containment pipe systems and thereby lower the overall cost to the system a need therefore exists for prefabricated pipe fittings, wherein the pipe fittings components are butt-welded together, thereby permitting complex fittings to be fabricated as modular components of either standard size or custom size of an overall double containment piping system.
The present invention is therefore directed to a prefabricated double containment pipe fitting and to a method, or a process, for fabricating double containment pipe fittings of higher structural integrity and to eliminate the need for costly field fabrication.
One principal aspect of the present invention accomplishes its intended purposes by providing a double containment pipe fitting in which the primary and secondary pipe portions of a double containment main pipe spool are butt-welded to opposing primary and secondary pipe portions of a double containment branch pipe spool simultaneously while a reliable butt-welded joint is effected where the opposing primary and secondary pipe portions of the main and branch pipe spools meet.
In another principal aspect of the present invention, a plastic first double containment pipe spool is joined to a plastic second double containment pipe spool at a specified angle from the longitudinal axis of the second double containment pipe spool by simultaneously contacting opposing faces of the first and second double containment spools to a heating assembly with opposing non-planar heating surfaces which are complementary to the opposing faces of the two pipe spools until the plastic melts, at which time the pipes are then pushed together and held in place until the plastic hardens to simultaneously create two distinct butt-welds one between the two primary pipe portions and the two secondary pipe portions of the respective first and second pipe spools.
In yet another principal aspect of the present invention, a double containment pipe reducing fitting comprises a main double containment pipe section having a reduced diameter branch double containment pipe section butt-welded to the main pipe section in which the endfaces of the branch section are cut at an angle and brought against a heating assembly male heating element while openings are cut in the main pipe section and then brought against a heating assembly female heating element located on the opposite side from the male heating element. These opposed male and female heating surfaces soften the plastic of the main and branch pipe section so as to permit them to be joined together to form the fitting.
In yet another principal aspect of the present invention, a method for fabricating a double containment pipe fitting includes providing a heating element having non-planar, opposed heating surfaces, cutting the edges of a first length of double containment pipe at a predetermined angle, cutting an opening in a second length of double containment pipe which is complementary to that of the first length, contacting the first and second pipe lengths against an angled heating element to soften the contact faces of the pipe plates lengths, joining the contact faces together and holding them together until the plastic solidifies.
Accordingly, it is an object of the present invention to provide a unique double containment fitting which can be easily fabricated in a factory to any desired field dimension so that the fitting can be used as a modular component 10, an overall double containment pipe system.
Another object of the present invention is to provide a method for assembly of a double containment pipe fitting wherein opposing contact faces are formed in two double containment pipe lengths, each pipe length having an inner primary pipe surrounded by an outer, secondary pipe in a spaced-apart relationship, and wherein a non-planar heating assembly is provided having opposed heating surfaces is moved into contact with the opposing contact faces, the opposing contact faces then being brought into the contact with the opposed heating surfaces and subsequently contacted together with each other.
Still another object of the present invention is to provide a thermoplastic double containment pipe fitting in which a branch fitting section is butt-welded to a header fitting section, each of the header and branch fitting sections having primary and secondary pipe portions, each of the header and branch fitting sections further having two distinct engagement surfaces defined along the primary and secondary pipe portions thereof, the header and branch fitting sections being butt-welded together along the header and branch fitting section engagement surfaces.
Yet another object of the present invention is to provide a unique, non-planar heating assembly for simultaneously heating endfaces of primary and secondary pipe portions of double containment pipe sections such that when their endfaces have softened to welding temperature, the endfaces of adjacent primary and secondary pipe sections can be joined together at an angle.
These and other features, objects and advantages of the present invention will become apparent from a reading of the following detailed description.